Petrology (from Greek: petra, rock; and logos, knowledge) is the branch of geology that studies rocks, and the conditions in which rocks form.

Petrology utilizes the classical fields of mineralogy, petrography, optical mineralogy, and chemical analyses to describe the composition and texture of rocks. Modern petrologists also include the principles of geochemistry and geophysics through the studies of geochemical trends and cycles and the use of thermodynamic data and experiments to better understand the origin of rocks.